Performing a Boiler Tune Up

1. The problem statement, all variables and given/known dataBTU input: 2.5 MMBtu/hr
Annual Gas usage: 8,525 MMBtu
Average Natural Gas Cost (Previous 12 months): $7.59/MMBtu Manufacturing Plant – 7am-7pm, 7 days/week, 50 weeks/yr
Assembly/warehouse - 7:00am-10:00pm, 7 days/week, 363 days/yr
The gas analyzer was used to check the O2 and temperature of the boiler exhaust during the on-site visit. The O2 level was found to be 10% and the exhaust temperature rise was 510°F.
a.) How would you go about doing a Boiler Tune up for the following system? Be specific to what values and specifications you alter.
b.) What is the cost savings from improving the efficiency. 2. Relevant equations
a.)b.)
ΔFuel Used = (new - old / new) (Old Fuel Used)

3. The attempt at a solution
a.) My recommendation is to lower the O2 level to 2% and lower the exhaust temperature rise to 87.5 to create an efficiency of 87.8% from the existing 81%. Is this possible and if so, does my readings seem right? I used the graph below. Also, is there anything else we can do to make it more efficient such as a different BTU input?
b.) (50 weeks * 7 days * 12 hours) = 4200 hours, & $7.59 MMBtu / 1.032 MCF = $7.35per MCF
(64,704.75 Cost Year) / (4200hrs)($7.35) = 2.0960 MCF per hour
Fuel Used = (87.8 - 81 / 87.8) (2.0960) = .162332 MCF per hourSavings = (.162332/hr)(4200 hrs/year)(7.35/MCF) = $5011/yr

I know this is a good bit of info in one problem, so I really do appreciate any feedback on this. Thanks so much.